The past tense of ride a horse foaled by an acorn is rode a horse foaled by an acorn or rid a horse foaled by an acorn.
The third-person singular simple present indicative form of ride a horse foaled by an acorn is rides a horse foaled by an acorn.
The present participle of ride a horse foaled by an acorn is riding a horse foaled by an acorn.
The past participle of ride a horse foaled by an acorn is ridden a horse foaled by an acorn.